AP Physics 1 : Motion in One Dimension

Study concepts, example questions & explanations for AP Physics 1

varsity tutors app store varsity tutors android store

Example Questions

Example Question #31 : Motion In One Dimension

A car is traveling on the freeway at \(\displaystyle 36 \frac{m}{s}\) when the driver sees traffic stopped \(\displaystyle 100 m\) ahead. What acceleration is needed to stop the car safely?

Possible Answers:

\(\displaystyle 6.5 \frac{m}{s^2}\)

\(\displaystyle -0.18 \frac{m}{s^2}\)

\(\displaystyle 0.18 \frac{m}{s^2}\)

\(\displaystyle 13.0 \frac{m}{s^2}\)

\(\displaystyle -6.5 \frac{m}{s^2}\)

Correct answer:

\(\displaystyle -6.5 \frac{m}{s^2}\)

Explanation:

We begin by noting we have been given no information about the time in which the stopping is to occur, only velocities and distance. This points us to the following kinematic equation:

\(\displaystyle V_f^2=V_i^2+2a\Delta x\)

By using the given information, and noting that coming to a stop implies a final velocity of \(\displaystyle 0 \frac{m}{s}\), we can directly substitute the numbers in and solve. It makes sense the final value is negative because the car is being accelerated in the negative direction in order to stop it.

\(\displaystyle a=\frac{-(36\frac{m}{s})^2}{2 (100m)}=-6.5 \frac{m}{s^2}\)

Example Question #301 : Ap Physics 1

 An airplane is flying at \(\displaystyle 37\frac{m}{s}\). It encounters a tailwind traveling at \(\displaystyle 9\frac{m}{s}\). At what speed is the airplane traveling?

Possible Answers:

\(\displaystyle 9\frac{m}{s}\)

\(\displaystyle 28\frac{m}{s}\)

\(\displaystyle 37\frac{m}{s}\)

\(\displaystyle 46\frac{m}{s}\)

Correct answer:

\(\displaystyle 46\frac{m}{s}\)

Explanation:

A tailwind is a wind traveling in the same direction as an object. The find the new speed of the airplane, we add the speed of the tailwind to the speed of the airplane.

\(\displaystyle \vec{v}= (37+9 )\frac{m}{s}=46\frac{m}{s}\)

Example Question #33 : Motion In One Dimension

A ball is dropped at time \(\displaystyle t=0\) from 20 meters above the ground. 

\(\displaystyle g=10\frac{m}{s^2}\)

How long does it take for the ball to hit the ground?

Possible Answers:

\(\displaystyle 8s\)

\(\displaystyle 2s\)

\(\displaystyle -2s\)

\(\displaystyle 1s\)

\(\displaystyle 4s\)

Correct answer:

\(\displaystyle 2s\)

Explanation:

Using the following kinematic equation:

 \(\displaystyle x=x_{0}+v_{0}t+\frac{1}{2}at^{2}\) 

\(\displaystyle x\) is the final position, in meters, (\(\displaystyle 0m\) for ground).

\(\displaystyle x_{0}\) is the starting position (\(\displaystyle 20m\) above ground)

\(\displaystyle v_{0}\) is the starting velocity  \(\displaystyle (0\frac{m}{s})\) because the ball is dropped and therefor starts from rest).

\(\displaystyle a\) is the acceleration due to gravity given by the problem statement.

Input these values into the first ruling equation and note that in this notation up is the positive direction so the acceleration due to gravity is negative:

\(\displaystyle 0m=20m+(0\frac{m}{s})(t)+\frac{1}{2}(-10\frac{m}{s^{2}})t^{2}\)

Then we solve for \(\displaystyle t\).

\(\displaystyle 0=20+0-5t^{2}\)

\(\displaystyle -20=-5t^{2}\)

\(\displaystyle 4=t^{2}\)

\(\displaystyle t=2s\)

Example Question #34 : Motion In One Dimension

A hot air balloon is rising at \(\displaystyle 2 \frac{m}{s}\) when a bag falls from the edge of the basket.

How far has the bag fallen from where it left the basket after 3 seconds? 

\(\displaystyle g=10\frac{m}{s^{2}}\)

Possible Answers:

\(\displaystyle 45m\)

\(\displaystyle 30m\)

\(\displaystyle 39m\)

\(\displaystyle 26m\)

\(\displaystyle 49m\)

Correct answer:

\(\displaystyle 39m\)

Explanation:

We use the equation:

\(\displaystyle x=x_{0}+v_{0}t+\frac{1}{2}at^{2}\) 

With \(\displaystyle x_{0}=0m\), \(\displaystyle v_{0}=2\frac{m}{s}\), \(\displaystyle a=-10\frac{m}{s^{2}}\), and \(\displaystyle t=3s\) we have:

\(\displaystyle x=0+3*2+\frac{1}{2}*-10*3^{2}\)

\(\displaystyle x=-39m\)

The bag has fallen 39 meters from its original position. Note that the question does not ask for the distance the bag is from the basket after 3 seconds so we do not have to take in to account how far the balloon has moved in the 3 seconds. Also, note that the question asks "how far" the bag is from the basket, so we do not have to worry about sign in the answer.

Example Question #35 : Motion In One Dimension

A rocket ship moves at \(\displaystyle 200\frac{m}{s}\)when a part breaks off and falls straight down. The rocket continues to move at the same velocity after the part breaks off.

How far below the ship is the part after 5 seconds?

\(\displaystyle g=10\frac{m}{s^{2}}\)

Possible Answers:

\(\displaystyle 875m\)

\(\displaystyle 1000m\)

\(\displaystyle 125m\)

\(\displaystyle 75m\)

\(\displaystyle 275m\)

Correct answer:

\(\displaystyle 125m\)

Explanation:

We use the equation:

\(\displaystyle x=x_{0}+v_{0}t+\frac{1}{2}at^{2}\) 

With \(\displaystyle x_{0}=0m\), \(\displaystyle v_{0}=200\frac{m}{s}\), \(\displaystyle a=-10\frac{m}{s^{2}}\) , and \(\displaystyle t=5s\) we have:

\(\displaystyle x=0+200*5+\frac{1}{2}*-10*5^{2}\)

\(\displaystyle x=875m\)

The part moves 875 meters upward in the time it breaks from the ship. Then, we use:

\(\displaystyle x=vt\) with \(\displaystyle v=200\frac{m}{s}\) and \(\displaystyle t=5s\) to find that the ship has moved 1000 meters during the same 5 second period.

So the ship moved upward 1000 meters in the 5 second time period while the part moved 875 meters upward so to find the distance between the ship and the part as the problem statement requested we subtract:

\(\displaystyle 1000m-875m=125m\)

Example Question #36 : Motion In One Dimension

A car moving to the right at \(\displaystyle 20\frac{m}{s}\) accelerates to the right at \(\displaystyle 3\frac{m}{s^{2}}\) for 14 meters.

What is the cars velocity after the acceleration period?

Possible Answers:

\(\displaystyle 26\frac{m}{s}\)

\(\displaystyle 20\frac{m}{s}\)

\(\displaystyle 29\frac{m}{s}\)

\(\displaystyle 18\frac{m}{s}\)

\(\displaystyle 22\frac{m}{s}\)

Correct answer:

\(\displaystyle 22\frac{m}{s}\)

Explanation:

We use the equation:

\(\displaystyle v_{f}^{2}=v_{0}^{2}+2ax\) 

Where the initial velocity is \(\displaystyle v_{o}=20\frac{m}{s}\), the acceleration is \(\displaystyle a=3\frac{m}{s^{2}}\) , and the displacement during the acceleration \(\displaystyle x=14m\).

Plug in those values into our equation and solve.

\(\displaystyle v_f^2=(20\frac{m}{s})^2+2*(3\frac{m}{s^2})*14m\)

\(\displaystyle v_f=\sqrt{400+84}=\sqrt{484}=22\frac{m}{s}\)

Example Question #37 : Motion In One Dimension

Calculate the acceleration, \(\displaystyle a\) of a race car that can go a distance of \(\displaystyle 1320ft\) in \(\displaystyle 3.5s\), assuming the acceleration is constant and the car starts from rest.

\(\displaystyle 1ft\approx 0.3048m\)

Possible Answers:

\(\displaystyle 215.5 \frac{m}{s^2}\)

\(\displaystyle 5.4\frac{m}{s^2}\)

\(\displaystyle 229.7\frac{m}{s^2}\)

\(\displaystyle 65.7 \frac{m}{s^2}\)

Correct answer:

\(\displaystyle 65.7 \frac{m}{s^2}\)

Explanation:

However unrealistic, if the acceleration of the race car were constant, we could calculate a value. We need everything in SI units, so we have to convert the distance to \(\displaystyle m\)

\(\displaystyle 1320ft\left(\frac{0.3048m}{1ft}\right )=402.3m\)

Using a kinematic equation, we can directly calculate the acceleration \(\displaystyle a\),

\(\displaystyle \Delta x = \frac{1}{2} a t^2 \Rightarrow a = \frac{2 \Delta x}{t^2}=\frac{2(402.3m)}{(3.5s)^2}=65.7\frac{m}{s^2}\)

Example Question #11 : Motion

A block is placed at a height of \(\displaystyle 18m\) on a ramp at an incline of \(\displaystyle 24^o\). It slides down from rest with an acceleration of \(\displaystyle 2.2\frac{m}{s^2}\) due to a frictional force. What is the velocity of the block when it reaches the bottom of incline?

24_deg._incline_block

Possible Answers:

\(\displaystyle v_f=5.1\frac{m}{s}\)

\(\displaystyle v_f=12\frac{m}{s}\)

\(\displaystyle v_f=8.9\frac{m}{s}\)

\(\displaystyle v_f=16\frac{m}{s}\)

\(\displaystyle v_f=14\frac{m}{s}\)

Correct answer:

\(\displaystyle v_f=14\frac{m}{s}\)

Explanation:

To find the final velocity we use the following kinematic equation.

\(\displaystyle v_f^2=v_o^2+2a\Delta x\)

The block starts from rest, so \(\displaystyle v_o=0\). The incline is eighteen meters high, so we can find the distance (hypotenuse) as follows:

\(\displaystyle \Delta x=\frac{18m}{sin24^\circ}\)

\(\displaystyle \Delta x = 44.25m\)

We know that the acceleration is \(\displaystyle a=2.2\frac{m}{s^2}\).

Plug in the values to find the velocity at the bottom of the incline.

\(\displaystyle v_f^2=(0\frac{m}{s})^2+2(2.2\frac{m}{s^2})(44.25m)\)

\(\displaystyle v_f=\sqrt{194.7\frac{m^2}{s^2}}=14\frac{m}{s}\)

Example Question #38 : Motion In One Dimension

Object A is traveling at \(\displaystyle < 10,0>\frac{m}{s}\). It is hit from behind by object B traveling at \(\displaystyle < 15,0>\frac{m}{s}\). If they both have a mass of \(\displaystyle 25kg\), determine their final velocity if they stick together.

Possible Answers:

\(\displaystyle < 15,15>\frac{m}{s}\)

\(\displaystyle < 12.5,0>\frac{m}{s}\)

\(\displaystyle < 0,0>\frac{m}{s}\)

\(\displaystyle < 0,12.5>\frac{m}{s}\)

\(\displaystyle < 15.0,0>\frac{m}{s}\)

Correct answer:

\(\displaystyle < 12.5,0>\frac{m}{s}\)

Explanation:

\(\displaystyle \overrightarrow{P}_{Total}=\overrightarrow{P}_1+\overrightarrow{P}_2...\)

Definition of momentum:

\(\displaystyle \overrightarrow{P}=m\overrightarrow{v}\)

Combine equations:

\(\displaystyle \overrightarrow{P}_{Total}=m_1\overrightarrow{v}_1+m_2\overrightarrow{v}_2\)

Plug in values:

\(\displaystyle \overrightarrow{P}_{Total}=25*< 10,0>+25*< 15,0>\)

\(\displaystyle \overrightarrow{P}_{Total}=< 250,0>+< 375,0>\)

\(\displaystyle \frac{\overrightarrow{P}_{Total}}{m}=\frac{< 625,0>kg\frac{m}{s}}{50kg}\)

\(\displaystyle \overrightarrow{v}=< 12.5,0>\frac{m}{s}\)

Example Question #39 : Motion In One Dimension

A ball is dropped from a building of height 45m. How long does it take for the ball to hit the ground? Ignore air resistance.

Possible Answers:

\(\displaystyle 3s\)

\(\displaystyle 2s\)

\(\displaystyle 9s\)

\(\displaystyle 5s\)

\(\displaystyle 10s\)

Correct answer:

\(\displaystyle 3s\)

Explanation:

Let's first list the values we know.

\(\displaystyle a=10\frac{m}{s^2}\)

\(\displaystyle v_o=0\frac{m}{s}\)

\(\displaystyle d=45m\)

We are looking for the time it takes for this ball to reach the ground, thus we are looking for \(\displaystyle t\). The kinematics equation we need to use is:

\(\displaystyle d=v_ot +\frac{1}{2}at^2\)

Since the initial velocity is zero, the \(\displaystyle v_ot\) term disappears. Thus we are left with:

\(\displaystyle 45m=\frac{1}{2}*10\frac{m}{s^2}t^2\)

Solve for time.

\(\displaystyle t=3s\)

We only take the positive value in our calculation since time cannot be negative. 

Learning Tools by Varsity Tutors